1. Field of the Invention
This invention relates to azo dyes and, more particularly, to reddish yellow cationic azo dyes characterized by their strong affinity for paper pulp.
2. Description of the Prior Art
Direct dyes for paper are well-known. Many of these dyes, however, when employed in conventional processes for dyeing paper, because of inadequate affinity for paper pulp, produce so-called white water containing environmentally significant amounts of the dyes. Ordinarily, the color must be destroyed before the white water can be discharged as effluent. The treatment of the white water is an additional and undesirable expense in the dyeing of paper.
There is, therefore, a great need for dyes for paper which have sufficient affinity for paper pulp such that the cost of treatment of white water is reduced or eliminated.
Moser, U.S. Pat. No. 3,933,787, discloses a process for the dyeing and printing of paper using azo dyes of the basic structural formula: ##STR2## where X is the radical of a coupling component of the aminobenzene, hydroxybenzene, aminonaphthalene or heterocyclic series.
It has now been found according to the present invention that certain cationic azo dyes wherein the base corresponds to that of the azo dyes of Moser, have excellent affinity for paper pulp under both sized and waterleaf dyeing conditions. These dyes enable the paper to be dyed even in heavy shades without any appreciable loss of dye in the white water. There is practically no dye left in the white water. The dyes also have fair to good fastness to acid, alkali and chlorine.
The coupler of the cationic azo dyes according to the present invention is disclosed in Renfrew, U.S. Pat. No. 3,881,866. The quaternary dyes of Renfrew which can include thiazoles or benzothiazoles as the base, are disclosed as having utility in the dyeing of acrylic fibers.